Method of blasting



Nov. 13, 1962 R. D. BODDORFF EI'AL 3,063,373

METHOD OF BLASTING Filed June 8, 1959 2 Sheets-Sheet 2 FIG. 4

FIG 5 POWER SOURCE FIG. 6

RAYMOND D. BODDORFF ROBERT W. LAWRENCE JUL! US ROTH INVENTORS BY q. PM

United States Patent ()fifice 3,063,373 latented Nov. 13., 1962 METHODOF BLASTING Raymond D. Boddorfi, Robert W. Lawrence, and Julius Roth,Wilmington, DeL, assignors to Hercules Powder Company, Wilmington, Del,a corporation of Delaware Filed June 8, 1959, Ser. No. 818,613 17Claims. (Cl. 102-23) This invention relates to a method for blasting ina borehole wherein the hole is filled wtih a gel disposed around adetonatable blasting charge so as to uniformly transmit energy from theblast to the borehole wall. In another aspect the invention relates to ablasting method above described wherein the blasting charge is detonatedby a fuse type detonator extending from the charge through the gel bodyto a point near the opening of the hole, the detonator fuse or cordbeing initiated at a point near its end extended from the charge wherebya particularly high efliciency of distribution of blasting energy to thehole Wall is accomplished. This application is a continuation-in-part ofour application Serial No. 520,760, filed July 8, 1955, now abandoned.

Since the early history of blasting operations, various cartridges havebeen suggested in which the explosive charge is surrounded by aflame-quenching material in order to adapt the charge for use in a minewhere inflammable gas is likely to be present. In earlier years, many ofthese cartridges employed water as the flamequenching material. However,these structures were not always satisfactory in view of the fact. thatthe outer container would often leak and thus permit the loss of theflame-quenching medium or else the water would find ingress into themain blasting .charge with deleterious elfect. Consequently, the morerecent development of the art has been to employ solid materials in theform of a sheath around the main explosive charge such as sodiumbicarbonate and the like.

More recently it has been realized that with more water-resistantexplosives, additional beneficial effect can be obtained by the use ofwater in a borehole as a means of hydraulically transferring the effectof the explosion to the wall of the borehole. This system of blasting isknown as pulsed infusion blasting, and has in recent years become quitepopular in Great Britain and on the continent. In accordance with thissystem, the explo-' sive charge is loaded in the hole and water isintroduced under pressure into the hole through a sealing plug. In viewof the fact that the rock formations often encountered in blastingoperations contain numerous fissures and cracks, it is necessary tomaintain the water under pressure until the explosive is actuallydetonated. Thus, large amounts of water are necessary and where thesefissures and cracks are numerous, the entire formation to be blasted issaturated with water, in many instances adversely affecting the entireoperation. Moreover, pressure-producing means are necessary and theadequate sealing of the mouth of the hole is difficult. Obviously, thepulsed infusion technique requires eon: siderable expensive equipment.In addition, the high pressure in the borehole requires the use ofspecial pressure resistant explosives which in some instances of suchoperations are uncertain in their action.

We have discovered that the principal benefits of pulsed infusionshooting can be obtained without saturating the formation to be blastedwith liquid and, moreover, without maintaining a fluid in the boreholeunder pressure at any time. The method of the invention, moreover, notonly uniformly transfers the force of the blast to the wall of theborehole but also gives considerably enhanced flame-quenchingcapabilities.

In accordance with the invention a blasting method is provided whichcomprises introducing into a borehole a detonatable blasting charge,having a volume substantially less than that of the said borehole, and anoncombustible nonexplosive gel; retaining said charge entirely Withinsaid borehole and disposing saidgel around said charge in sufiicientamount to also substantially fill the remaining space in said borehole;and then detonating said charge. H V V I p The blasting charge can bedetonated by anysuitable means including detonating fuse such asPrimacord of Cordeau, electrie blasting caps, or combinations ofdetonating fuse and blasting caps. However, as described hereinafter, adetonating fuse connected with the explosive charge, and extending fromthe charge through the gel column to substantially the mouth of thehole, is preferred, in which embodiment a suitable detonating means forinitiating detonation of the detonator cord is afiixed in detonatingrelationship with the cord at the end thereof nearest the mouth of thehole. I

The invention is further illustrated with reference to FIGS. 1-6 of thedrawings of which FIGS. l-3 and 4'6, respectively, illustrate separatevmethod embodiments. FIGURE 7 is the same as FIGURE 6 except that it isillustrative of method employing a borehole extending upwardly from thehorizontal. In FIG. 1, a cartridge 10 of permissible dynamic primed witha length of detonating fuse 11, such as Primacord, has been insertedinto a borehole 12. The fuse 11 is in turn primed with an electricblasting cap 13, the lead wires of which extend from the hole. In FIG.2, atube 20 for delivery of gel into the borehole has been inserted intothe borehole, preferably as far back into the hole as possible and a nonexplosive gel 21 is pumped v by pump means 22 through tube 20 into thehole. As the hole fills with the gel 21, the tube 20 is forced therefromand the hole isfilled substantially to the mouth. The gel is forced bypump means 212 into thehole and around the charge 10. In FIG. 3, theloaded hole is sealed by means of a conventional tamping plug 30 such asan asbestos tubular cylinder 31 with conical insert32. The tubularcylinde'r 31 is initially positioned in the mouth of the hole 12 and theconical insert is then driven into the cylinder 31 to expand thecylinder, thus sealing the mouth of the hole around the lead wires 14.When the cartridge 10 is detonated by initiating detonation of the fuse11 by means of the blasting cap'13, the" energy from the 6X-, plodi igcartridge and fuse is transmitted to the wall of the borehole throughthe medium of the gel, to produce lump coal of improved uniformity insize. v I

In accordance with thenow preferredmethodembodimerit of the invention, afuse type detonator isaffixetl to ade tonatable explosive charge, as bytaping, and the detonating fuse is extended from the charge to a pointin close proximity to the mouth of the liole, at which point a suitabledetonator for the detonating fuse, for example, an electric blastingcap, is affixed, but at a point still within the borehole. The leadwires, or, other line of communication for the detonator, extend fromthe open end of the hole to a suitable energy source. Preferably thehole is closed at the mouth by a' tamping plug" 30 after introduction ofthe gel as illustrated with reference to FIGURES 3 and 6 of thedrawings.

In order to assure cqmplete filling of the holes with gel so as tominimize possibility for the presence of air pockets, it'is advantageousto first fill the hole 12' with a gel 21 up to a point near the mouth21, as shown with reference to FIGURE 4. A detonating' fuse, e.g., 50grain Primacord, is's'ecured at one end of the main deto hat-able charge10 as by a loop with taping as illustrated with reference to FIGURE 5although, of course, any suitable means for securing the detonating fuseto the cartridge can be employed, such as tapingas illustrated withreference to FIGURE 6, fuse 11 being thereby afiixed in detonatingrelationship with main charge 10. Fuse 11 is affixed at its end oppositecharge with an electric blasting cap 13 in detonating relationshiptherewith. The resulting cartridge-fuse-blasting cap assembly is theninserted, cartridge first, into borehole 12 through the gel column 21 toany suitable point preferably so that the main charge 10 is disposed inthe closed end of the borehole as illustrated with reference to FIGURE6. Any suitable means, for example, a small diameter wood rod, can beutilized for directing the primed cartridge assembly of FIGURE 6 intothe desired position. The length of detonating fuse 11 of FIGURE 6 issufficient if it extends from cartridge 10 in borehole 12 to a point inclose proximity to the mouth 21 but at a length sufficient to permitenclosure of blasting cap 13 attached thereto within borehole 12 andadjacent plug 30 when the latter is utilized. Generally, when utilizinga plug 30, termination of fuse 11 at a point say about 6-8 inches fromthe open end of borehole 12 to allow for insertion of closure plug 30 issufficient. Lead wires 14 extend from the borehole 12 through the openend thereof to a suitable power source. When closing the mouth of theborehole with a closure plug such as plug 30 of FIGURE 3, the lead wires14 extend from the borehole intermediate the plug assembly and the holewall as illustrated with reference to FIGURES 3 and 6.

Although the entire assembly of FIGURE 6 is preferably assembled byfirst loading the gel followed by insertion of the primed chargeassembly as above described to minimize air pockets, the gel can becharged subsequent to insertion of the cartridge assembly as illustratedwith reference to FIGURES 1 to 3.

FIGURE 7 illustrates practice of the invention as applied to blasting ina borehole inclined above the horizontal, generally, 20 to 30 degrees,and is otherwise in all respects the same as FIGURE 6. The single primednumerals, and numeral 21", of FIGURE 7 correspond respectively to thesame numbers unprimed, and to 21, of FIGURE 6.

The following examples are presented as illustrative of preferredembodiments of the invention.

Example 1 A hole 7 feet deep and 1.75 inches in diameter was drilled ina coal face 3 feet above an undercut in a coal seam. Three 1% in. by 8in. cartridges of a permissible explosive were taped to one end of a6-ft. length of 50 grain Primacord. An electric blasting cap was tapedto the other end of the Primacord. The primed cartridges of dynamitewere inserted in the hole and about 2.8 liters of a gel consisting ofwater, 0.5% carboxymethylcellulose and 0.1% AI (SO was forced into thehole by compressed air. When the hole was filled to the 6-ft. mark, aconventional tamping plug was inserted and expanded. When the dynamitewas shot, coal was brought down in excellent lump size with a remarkablereduction in dust, smoke and fumes as compared to a conventional shot.

Example 2 A shot was loaded similar to that in Example 1, except thatonly two 1% in. by 8 in. cartridges of the permissible explosive wereemployed. This shot again brought down the coal in excellent lump sizewith a remarkable reduction in dust, smoke and fumes.

Example 3 p A third hole similarly disposed was loaded with threecartridges of the permissable dynamite which were taped to one end of a2-ft. length of Primacord. An electric blasting cap was taped to theother end of the Primacord. The gel was similarly introduced and thehole sealed with the tamping plug. Again the shot brought down coal inexcellent lump size with a similar reduction in dust. smoke and fumes.

Example 4 A fourth hole of the same dimensions was similarly shot exceptthat two 1 in. by 8 in. cartridges of the permissible dynamite weretaped to one end of a 2-ft. length of Primacord. The gel was similarlyintroduced and the hole sealed with a tamping plug. Once more this shotbrought the coal down in excellent lump size with great reduction indust, smoke and fumes.

Although in the practice of the invention transmission of energy to thehole walls is effected by detonating the main charge in any suitablemanner, superior results are obtained when employing a detonating fusefor detonation of the main charge. It appears that a detonating fusefunctions by release of energy from its own detonation along theborehole length to unexpectedly facilitate uniform transmission ofenergy from detonation of the main charge to the Wall and therefore forimproved amount and quality of breakdown. The following exampledemonstrates the unique function of a detonating fuse in the practice ofthe invention.

Example 5 A series of three blasting tests was conducted, in each ofwhich a permissable dynamite was detonated in a coal formation ingel-filled boreholes. In one of the tests the dynamite charge wasdetonated by action of an electric blasting cap only, and in theremaining tests the dynamite was initiated by detonating action ofvarying lengths of Primacord, the cord extending substantially to themouth of the borehole in the one instance and through only a portion ofthe hole in the other.

In each test three spaced apart boreholes were filled with a thixotropicgel consisting of 88-89% water and 11-12% bentonite. Each of the nineholes shot was 6 /2 ft. in length. The coal face in each test was 10 ft.wide and 5 /2 ft. high with an undercut 7 ft. deep and 8 in. high.

In each of the tests an effectiveness factor was determined as a measureof the efficiency of energy distribution obtained, the higher thenumerical value of the factor, the greater the efficiency of energydistribution. The said factor was calculated by multiplying the productof (1) coal production factor (the ratio of coal loosened by blasting tothe total coal in the cut, i.e., 10 ft. x 5V2 ft. x 7 ft. 8 in. abovedescribed), (2) breakage factor (the ratio of coal breakage exceedingthree inch lump to the coal loosened by the blasting), and (3) powderfactor (ratio of tons of coal loosened to pounds dynamite detonated), bya volume correction, namely, the ratio of the volume of a standard cutwhich is in. wide by 84 in. deep by 66 in. high, to the volume of thecut tested.

Data summarizing these tests are tabulated as follows:

Main explosive harge 2 Length of Detonat- Effec- Test No. ing Fusetiveness Cartridge Elrnployed, Factor Total Dimcn- Inches Wt., lbs.sions,

inches 2. 4 1% x 16 0 1. 2 2. 4 1% x 16 16 1. 6 2. 4 1% x 16 55 2. 3

A No. 6 electric blasting cap utilized to directly detonate the maincharge in test 1 and the Primacord in each of tests 2 and 3.

{A permissible dynamite-8,200 itJsec. detonation velocity; 60 percentweight strength; 44 percent volume strength.

3 Primacord, 50 grains PETN per foot.

In tests 1, 2 and 3 the effectiveness factor increased from 1.2 to 1.6to 2.3 when, respectively, no detonating fuse cord was used, the cordwas 16 inches in length, and 55 inches in length. Without use of thedetonating fuse, the said factor averaged about 1.1. The magnitude ofthe effectiveness factor thus shown expresses the effectiveness of theexplosive charges in the blasting of lump coal and 5. the markedlyimproved energy transmission to the bore? hole wall that is obtainedwhen a detonating fuse is utilized for detonation of the dynamitecharge. Thus, the highest effectiveness factor, 2.3, was observed whenutilizing a 55-inch length of, detonating fuse under which conditionsexceptionally high quality lump breakage with minimum formation of fineswas obtained. when the dynamite charge was detonated by electricblasting cap only, a satisfactory breakage was obtained but wasaccompanied by considerably higher yields of fines and a broadergradation of lump coal as demonstrated by the eifectiveness factor oftest 1. The unpredicted function of the detonating fuse is furtherdemonstrated by a cornparison of tests 2 and 3 which show an increase ineffectiveness factor with increased length of detonating fuse utilized.

Although a permissible dynamite was employed in shooting down coal inthe practice of the process exemplified hereinabove, it is to beunderstood that the present invention is not limited to coal miningoperations or to the use of permissible explosives.

Any suitable means for charging the gel to the borehole can be utilized.In Examples 13 the gel was introduced into the hole by means ofapressure cylinder filled with compressed air which exerted air pressureupon the gel in a reservoir and forced it through the tube and into thehole. In Example 4 and 5 the gel, in all tests, was charged by positivedisplacement pump. The hole in the tests of Examples 4 and 5 waspartially filled with the gel and the cartridge and detonator assemblythen inserted through the gel body into position for shooting followedby filling the remaining hole space with gel and insertion of a stemmingplug.

While bentonite gel is now prefer-red both from the standpoint ofeconomy and operation, and a gel comprising water,carboxymethylcellulose and a precipitating agent such as aluminumsulfate can be advantageously employed, other gelling agents can beutilized. Agents suitable for gelling water include:

Bentonite u i l Watef soluble cellulo sics such ascarboxymethylcellulose,

sodium carboxymethylcellulose, methyl cellulose, hydroxymethyl andhydroxyethyl cellulose, and cellulose sulfate.

Polyvinyl alcohol Polyacrylic acid, its copolymers and salts Copolymersof maleic anhydride with styrene or vinyl acetate Sodium vinyl sulfonateAlginates Starch Natural gums such as guar Psyllium seed Locust beanIrish moss Animal proteins such as gelatin, glue or casein It is, ofcourse, desirable to the economy and simplicity of the operation thatagents be chosen which require only small amounts to produce a gel ofthe desired viscosity. Preferably, the gel will have a viscosity suchthat it will remain in a hole even when the hole is inclined from 203()above the horizontal.

As illustrated, the use of a tamping plug is desirable but notessential, since the gel transmits the force of the explosion orexpanding gases to the Wall of the hole before it is forced out of theborehole at the instant of the shot. Moreover, it will be seen that theuse of a gel instead of water obviates the necessity of saturating theentire strata with fluid, the necessity of maintaining the fluid underpressure and the necessity of practically hermetically sealing the mouthof the borehole. The advantages of the invention are multiplied as thenumber of holes is increased. Thus, all of the advantages of the use ofa fluid are obtained with much greater economy 6 and facility in theblasting-operation. The reduction in smoke and fumes, moreover, makes itpossible to employ the process of the invention in on-shift operationsand, moreover, permits miners engaged in tunnel operations to return tothe scene of the blast much sooner than with permissible explosivescurrently employed. The method of the invention may be employed inmultiple hole shooting with either regular or short period delaytechniques.

Since many modifications mayobviously be made in the invention asdisclosed, it is intended that the scope of the invention shall belimited only by the appended claims. What we claim and desire to protectby Letters Patent 1s:

1. A method for blasting coal deposits which comprises forming anelongated borehole in a coal deposit, introducing into said borehole, aselements of a'blasting system therein, a detonatable blastingcharge,'having a volume substantially less than that of the saidborehole, and a noncombustible nonexplosive gel; retaining said chargeentirely within said borehole and disposing said gel around said chargeinsufficient amount to also substantially fill the remaining space insaid borehole; and then detonating said charge.

2. In a blasting method of claim 1, closing the mouth of said boreholeprior to detonating said charge.

3. A blasting method of claim 1 wherein said borehole is first filledwith said gel and said charge is then introduced through the gel bodyinto the said borehole.

4. A blasting method of claim 1 wherein said charge is introduced intosaid borehole prior to introduction of said gel into said hole.

5. A blasting method of claim 1, wherein said blaste ing charge is adynamite, affixing a detonating fuse to said dynamite charge ofsufiicient length to extend'from said dynamite charge to a point withinsaid borehole in close proximity to the open end thereof, and initiatingsaid dynamite charge by detonating said fuse at its end near theborehole open end.

6. A method of claim 1 wherein said gel is formed from water andbentonite;

7. A method for blasting coal deposits which comprises substantiallyfilling a borehole in a coal deposit with an acqueous noncombustiblenonexplosive gel; atfixing to a dynamite cartridge a detonating fuse ofsufficient length to extend from said cartridge as described hereinafterand afiixing blasting cap means for detonating said fuse to the endthereof opposite said cartridge; introducing the resulting primedcartridge assembly, cartridge first, into said borehole toward theclosed end thereof through the column of gel therein so as to disposesaid cartridge in said hole surrounded by said gel, and extending saiddetonating fuse and blasting cap means afiixed thereto from saidcartridge to a point within said hole in close proximity to the mouththereof, positioning a closure plug in said hole at the mouth thereofand extending lead wires from said blasting cap means from the boreholeintermediate said plug and the borehole wall into communication with asuitable power source for initiating said blasting cap means; and thendetonating said charge by electrically initiating said blasting capmeans, whereby coal deposits in the area of said hole are brought downin uniform lump size; and recovering lump coal product so produced.

8. A method of claim 7 wherein said gel comprises bentonite and water.

9. A method for blasting coal deposits to produce lump coal, comprisingafiixing a detonating fuse to a dynamite cartridge; afiixing an electricblasting cap to the remaining unattached end of said fuse; forming anelongated borehole in a coal deposit; inserting the resulting primedcartridge assembly into the said borehole; introducing a noncombustiblenonexplosive gel into said hole around said cartridge and in an amountto substantially fill said hole; closing the resulting filled hole witha closure plug and detonating the dynamite charge by initiating saidblasting cap, whereby coal deposits in the area of said hole are broughtdown in uniform lump size.

10. A method of claim 7 wherein said borehole extends into said depositat an angle of from about to above the horizontal, and said gel isformed from bentonite and water.

11. A method for blasting coal deposits which comprises forming anelongated borehole in a coal deposit substantially filling said boreholein a coal deposit with an aqueous noncombustible nonexplosive gel;affixing a detonating fuse to a dynamite cartridge and afiixing blastingcap means for detonating said fuse to the end thereof opposite saidcartridge; introducing the resulting primed cartridge assembly,cartridge first, into said borehole toward the closed end thereofthrough the column of gel therein so as to dispose said cartridge insaid hole surrounded by said gel, and then detonating said charge byelectrically initiating said blasting cap means, whereby coal depositsin the area of said hole are brought down in uniform lump size; andrecovering lump coal product so produced.

12. A method of claim 11 wherein said borehole extends into said depositat an angle of from about 20 to 30 above the horizontal, and said gel isformed from bentonite and water.

13. In a method of claim 9, extending said fuse in said borehole fromsaid dynamite cartridge to a point in close proximity to the mouth ofsaid borehole.

14. A method for blasting goal deposits to produce lump coal, comprisingafiixing a detonating fuse to a dynamite cartridge; affixing an electricblasting cap to the remaining unattached end of said fuse; forming anelongated borehole in a coal deposit inserting the resulting primedcartridge assembly into the said borehole; introducing a noncombustiblenonexplosive gel into said hole around said cartridge and in an amountto substantially fill said hole; and detonating the dyanmite charge byinitiating said blasting cap, whereby coal deposits in the area of saidhole are brought down in uni form lump size.

15. A method for blasting coal deposits which com-- prises forming anelongated borehole in a coal deposit, introducing into the saidborehole, as elements of a blasting system therein, a detonatableblasting charge, having a volume substantially less than that of thesaid borehole, and a noncombustible nonexplosive gel formed from waterand carboxymethylcellulose with a minor proportion of a suitableprecipitating agent therefor; retaining said charge entirely within saidborehole and disposing said gel around said charge in sufficient amountto also substantially fill the remaining space in said borehole; andthen detonating said charge.

16. The method of claim 15 wherein said precipitating agent is aluminumsulfate.

17. A method for blasting coal deposits which comprises substantiallyfilling a borehole in a coal deposit with an aqueous non-combustiblenon-explosive gel formed from water and carboxymethylcellulose with aminor proportion of a suitable precipitating agent therefor; affixing toa dynamite cartridge a detonating fuse of sufficient length to extendfrom said cartridge as described hereinafter and aflixing blasting capmeans for detonating said fuse to the end thereof opposite saidcartridge; introducing the resulting primed cartridge assembly,cartridge first, into said borehole toward the closed end thereofthrough the column of gel therein so as to dispose said cartridge insaid hole surrounded by said gel, and extending said detonating fuse andblasting cap means afiixed thereto from said cartridge to a point withinsaid hole in close proximity to the mouth thereof, positioning a closureplug in said hole at the mouth thereof and extending lead wires fromsaid blasting cap means from the borehole intermediate said plug and theborehole wall into communication with a suitable power source forinitiating said blasting cap means; and then detonating said charge byelectrically initiating said blasting cap means, whereby coal depositsin the area of said hole are brought down in uniform lump size; andrecovering lump coal product so produced.

References Cited in the file of this patent UNITED STATES PATENTS Re.20,412 Salvatori June 15, 1937 1,042,643 Brunswig Oct. 29, 19121,473,596 Lisse Nov. 6, 1923 2,034,568 Ferrell et al Mar. 17, 19362,316,596 Kennedy Apr. 13, 1943 2,816,071 Watkins Dec. 10, 1957 FOREIGNPATENTS 5,222 Great Britain of 1886

1. A METHOD FOR BLASTING COAL DEPOSITS WHICH COMPRISES FORMING ANELONGATED BOREHOLE IN A COAL DEPOSIT, INTRODUCING INTO SAID BOREHOLE, ASELEMENTS OF A BLASTING